In the practice of medicine, four measurements have long served as indicators of the body’s basic functions: pulse, breathing, temperature, and blood pressure.

In 1999, the Veterans Health Administration — the country’s largest government-run health care system — proposed a fifth vital sign: pain. The concept was initially promoted by the American Pain Society.

The VA launched an initiative to routinely assess pain, asking patients to measure their discomfort on a scale of 1 to 10, in response to a perception that veterans’ pain was undertreated. The result was the pain rating scale — depicting a smiling face for “no pain” to a grimacing, crying face for “worst possible pain” — seen today on the walls of so many hospitals and doctor’s offices.

The “Pain as the Fifth Vital Sign” effort also directed VA health providers, through a national policy, to document treatment plans for alleviating patients’ pain.

The Joint Commission, an organization that accredits health care organizations, soon followed suit. Many doctors began, for the first time, to view pain as a measurable symptom that should be documented and treated. Many also feared that failing to treat pain could lead to accusations of substandard care.

At the same time, pharmaceutical companies were developing new narcotic painkillers such as OxyContin. Evolving attitudes toward treating pain — both within and outside the VA — combined with the availability of powerful new medications to alleviate it led to an explosion of prescriptions.

More than a decade later, it became clear the practice led to a wave of addiction, and bore out the dangers of freely treating pain with addictive medication without measuring the impacts.

Today, the VA remains a top prescriber of powerful opiate painkillers nationwide. In Maine, the VA system issues almost 10 percent of all controlled substances.

The reasons are many. New treatments and better combat armor allow soldiers to survive once-fatal traumatic injuries, but leave them in pain, according to a 2013 investigation by the Center for Investigative Reporting. Lack of coordination among doctors can leave patients with multiple prescriptions for pain drugs, while some veterans misuse medications prescribed for physical injuries to treat the emotional wounds of war, the investigation found.

A decade after its Pain as the Fifth Vital Sign initiative, the VA issued new regulations, directing clinicians to take an “integrated” approach toward treating veterans in pain. The regulations called for more focus on treating the root causes of pain, rather than simply relying on narcotics to dull the symptoms.

Adoption of those regulations varies wildly, according to the CIR investigation.